1. Field of the Invention
The present invention relates generally to ceramic fiber insulation, and more particularly to methods and coatings for use with the same.
2. Description of Related Art
In many industrial applications it is necessary that conduits or ducts be provided for interconnection of various types of apparatus which require the routing of hot atmospheres or gases of many chemical compositions from one component to another. In most of these environments, the hot gases exhibit not only corrosive characteristics which will adversely affect conventional metallic conduits, but are also caused to flow at relatively high velocities. The relatively high gas flow velocity frequently encountered results in further adverse effects of frictional wearing and erosion of the interior of metallic ducts or other types of ductwork including but not limited to the increased likelihood of chemical corrosion. The relatively high temperatures also have a substantial adverse effect on the metal conduit such as decreasing structural strength and presenting a safety hazard to workers who may need to be in close proximity.
One technique heretofore utilized to meet the requirements of this highly adverse operational environment has been to line metallic or steel ducts with a castable refractory material. A disadvantage of the ducts having the castable refractory liner is that such refractories are not thermally efficient and as a consequence, the metal ducts which are lined with such materials must be made so as to develop greater structural strength to support the weight of the castable refractory that is required in most cases to meet the operational requirements.
There has also been an attempt to form ducts capable of withstanding the operational requirements of transmission of hot gases by lining metal conduits with a soft ceramic fiber material. The soft ceramic fiber material, as its name implies, does not exhibit the desired resistance characteristics to erosion by the relatively high gas velocities that are encountered. In an effort to meet the erosion effect, there have been attempts to also coat the interior surface of these liners with a layer of suitable material to attempt to rigidify the interior surface layers. These attempts have also not proven to be sufficiently successful as the rigidifying surface material will eventually crack and peel off and expose soft ceramic fibers to the point where the liners will erode and eventually become unusable, thus requiring replacement.
Another disadvantage of either the castable refractory liners or the soft ceramic fiber lining is the technique of obtaining the attachment or positioning of the liner within the metal conduit. The usual techniques require first securing of anchors to the interior of the metal duct. The refractory material is then either mechanically secured or it is formed directly onto those anchors such as by spraying or molding. Similarly, the soft ceramic fiber linings have been applied to the interior of the metal conduits by use of anchors which are first secured to the interior of the metal conduit.
Another attempt to meet the problems has been the formation of a vacuum cast sleeve or liner which is then subsequently assembled with a metal duct. This technique is not particularly advantageous in that it requires assembly at the operational site where the duct will be utilized. This technique increases the cost of installation.
In order to meet fire codes in terms of fireproof and fire resistance protection, insulation products must either have substantial mass or be endothermic in nature. Therefore, many insulation products must be treated or fabricated in such a way so as to give them such properties. Many endothermic materials are known. However, there are still problems associated with such materials and it would be desirable to have a material that is advantageous in terms of its end use properties and its ease of manufacture.
In accordance with these and other objectives, the present invention is directed to ceramic fiber insulation and related products and methods. The present invention further is directed to a ceramic coating that is capable of being brushed and/or sprayed lightly as a liquid onto vacuum-formed ceramic fiber insulation for use at high temperatures.
In a preferred embodiment, the instant invention provides a method for making refractory linings and insulation products wherein a ceramic fiber sleeve is positioned in and retained without the need for expansion joints and, in most applications, without utilization of mechanical attachment anchors, however the instant invention also contemplates the use of expansion joints and anchors as well. Preferred embodiments of the instant invention also provide ceramic fiber linings capable of handling gases of relatively high temperatures.
The instant invention also provides a ceramic fiber lined duct comprising a vacuum-formed ceramic fiber liner that has been treated with a coating affixed to a metal jacket.
In another preferred embodiment, the instant invention provides a method of making a duct capable of handling gases of relatively high temperatures and also having fire resistant, erosion resistant, and corrosion resistant properties fabricated by first forming a ceramic fiber sleeve and, while the sleeve is in a wet or hydrated state, positioning the sleeve within a metal tube and thereafter subjecting the assembly to a drying operation to remove moisture from the ceramic fiber sleeve. This method results in the sleeve and metal tube being mechanically and adhesively secured together into assembled relationship.
In another preferred embodiment, the instant invention provides a method of vacuum-forming a ceramic fiber insulation or lining conforming to the size and shape of a particular fitting or commercial heating component and positioning it within a metal jacket similarly to a ceramic fiber sleeve within a metal tube.
In another preferred embodiment, the instant invention provides a xe2x80x9cclamshellxe2x80x9d method for making ceramic fiber-lined metal-jacketed fittings or ducts of complex shapes which cannot be made with a single vacuum-forming operation. This involves forming sections or half sections of such a fitting or duct and combining them so as to make one complete fitting.
In another preferred embodiment, the instant invention provides a method for making refractory linings and insulation products wherein materials such as, but not limited to, mineral wool and/or graphite felt can be used in place of or in addition to ceramic fiber within the metal jacket of a duct, fitting or commercial heating component.
The instant invention also provides a refractory lining comprising a vacuum-formed ceramic fiber liner that has been treated with a coating. In a preferred embodiment, the instant invention provides a method of increasing fire resistance, thermal resistance, erosion resistance, and corrosion resistance of a vacuum-formed ceramic fiber lining comprising treating said ceramic fiber lining with a coating on a surface of said ceramic fiber insulation, wherein said coating renders said duct capable of being used at temperatures from about 2,300xc2x0 F. to about 3,000xc2x0 F.
In addition to the above applications, the coating""s fire resistance, as opposed to merely heat resistance, as well as the coating""s erosion resistant and corrosion resistant properties, make the present coating a desirable coating for vacuum-formed ceramic fiber products. In this case, as in the above applications, the coating would preferably be brushed and/or sprayed lightly onto the hot face of ceramic fiber insulation, whether or not the insulation contains an outer steel jacket.
Additional objects, features and advantages of the invention will be set forth in the description which follows, and in part, will be obvious from the description, or may be learned by practice of the invention. The objects, features and advantages of the invention may be realized and obtained by means of the instrumentalities and combination particularly pointed out in the appended claims.